The present invention relates to a manifold gasket for an internal combustion engine, which is immovably situated between a cylinder head and a manifold by means of bolts attached to the cylinder head passing through the manifold and the manifold gasket to thereby prevent an exhaust gas from leaking between the cylinder head and the manifold.
An automobile engine has been developed to become light in weight and small in size as well as to increase power. In order to satisfy these demands, an aluminum alloy is employed as a cylinder head, and the manifold is made thinner than before. Since the cylinder head is made of an aluminum alloy, the cylinder head expands due to high temperature when the engine is operated and contracts when the engine is stopped to thereby become cool in temperature. Further, since the manifold is made thin, a manifold flange slightly deforms by high temperature when the engine is operated. Also, the manifold gasket is cyclically exposed to high and low temperature according to operation and non-operation of the engine.
Due to the reasons as mentioned above, i.e., the cylinder head cyclically expands and contracts, the manifold slightly deforms when the engine is operated and the manifold gasket is cyclically exposed to high and low temperature, a conventional manifold gasket receives a stress to thereby be damaged or to be unable to provide proper seal because of insufficient seal pressure applied to the manifold gasket to cause problems, such as leakage of an exhaust gas.
Various types of gaskets have been proposed and used. One type of gasket is basically made of an asbestos and known as an asbestos gasket. This asbestos gasket, however, can not be used as a manifold gasket for a light weight and high power engine, because the recent engine exerts special stress to the manifold gasket as explained before. The manifold gasket made of an asbestos can not seal properly.
Another type of gasket is made of a metal and known as a metal gasket. A steel laminate gasket, one of metal gaskets, when compared with other metal gaskets, has good flexibility and heat resistance. Further, the steel laminate gasket with a bead therein possesses sufficient compression ability, when being tightened, to thereby provide good sealing ability by counteraction of the bead. Also, the sealing ability does not change as time goes by. The steel laminate gaskets are generally used for cylinder head gaskets of diesel engines, as shown in FIGS. 1-3.
The steel laminate gasket 10 is situated between a cylinder head and an engine body and includes at least one hole 11, through which a piston reciprocates. The gasket 10 as shown in FIG. 1 is provided with outer plates 12, 13, and two inner plates 14, 15 having bead portions 14a, 15a to surround the hole 11. Partition plates 16, 17 are respectively situated between the outer plate 12 and the inner plate 14, and between the outer plate 13 and the inner plate 15, while the partition plate 18 is situated between the two inner plates 14, 15.
The outer plate 12 is curved at a curved portion 19 adjacent to the hole 11 and turned to be situated over the periphery of the outer plate 13 at a flange 20 thereof. When the gasket 10 is situated and tightened between the cylinder head and the engine body, the curved portion 19 seals around the hole 11 and, the bead portions 14a, 15a springly support the flange 20 and the outer plate 12.
A steel laminate gasket 21, as shown in FIG. 2, is provided with outer plates 22, 23, and an inner plate 24 having a bead portion 24a to surround the hole 11. A partition plate 25 is situated between the outer plate 22 and the inner plate 24, while a partition plate 26 is situated between the outer plate 23 and the inner plate 24. The outer plate 22 is curved at a curved portion 27 adjacent to the hole 11 and is turned to be situated over the periphery of the outer plate 23 to form a flange 28. When the gasket 21 is situated and tightened between the cylinder head and the engine body, the curved portion 27 seals around the hole 11, and the bead portion 24a springly supports the flange 28 and the outer plate 22.
A steel laminate gasket 30, shown in FIG. 3, is provided with two outer plates 31, 32, and an inner plate 33 having a bead portion 33a. Plates 34, 35, 36 are arranged between the outer plates 31, 32 as shown in FIG. 3. The gasket 30 is further provided with a ring 37 having flanges 38, 39 and a curved portion 40. The flanges 38, 39 are situated outside the outer plates 31, 32, and the curved portion 40 is located adjacent to the hole 11. When the gasket 30 is situated and tightened between the cylinder head and the engine body, the curved portion 40 seals around the hole 11, and the bead portion 33a springly supports the flanges 38, 39 of the ring 37.
The steel laminate gaskets having the structure as explained above can be properly used as cylinder head gaskets. However, the steel laminate gaskets as shown in FIGS. 1-3 can not be used as manifold gaskets in a light weight and high power engine developed recently.
For example, if the steel laminate gasket 21 as shown in FIG. 2 is used as a manifold gasket in a high power engine, the cylinder head H and the manifold M expand and contract as shown at arrows in FIG. 4 due to heat of the engine in compliance with operation or non-operation of the engine. Further, since the flange 28 and the outer plate 22 are securely connected to the manifold M and the cylinder head H respectively, when the cylinder head H and the manifold M expand and contract, the curved portion 27, which is a sealing portion of the gasket 21, is exposed to high stress to thereby develop fatigue to the curved portion 27. Consequently, a crack may occur in the curved portion 27. Further, when the flange 28 and the outer plate 22 are moved together with the cylinder head H and the manifold M, the curved portion 27 or the outer plate 23 is deformed (FIGS. 4A and 4B), so that such portions are finally broken.
The reason that the steel laminate gasket which can be properly used as a cylinder head gasket can not be used as a manifold gasket is that the cylinder head gasket can be tightened stronger than the power exerted on the manifold gasket. Further, since the rigidity of the gasket attaching portions of the cylinder head gasket is made stronger than that of the manifold gasket, the gasket attaching portions do not significantly deform. On the contrary, the gasket attaching portion for the manifold gasket in the recent engine is made thin for making the engine light in weight and small in size. Accordingly, the gasket attaching portion for the manifold gasket can not be strongly tightened and slightly deforms by heat of the engine. Namely, the cylinder head gasket is located in a better place for sealing than the manifold gasket. The manifold gasket in the recent engine must have specific characteristics adapted to be used in a bad sealing condition. The manifold gasket can not be substituted by any other gasket.
Accordingly, one object of the present invention is to provide a manifold gasket having a sufficient sealing ability in a severe condition in use caused by a light weight and small size engine developed recently.
Another object of the present invention is to provide a manifold gasket as stated above, wherein the manifold gasket can be sufficiently sealed by a relatively small amount of pressure applied thereto.
A further object of the present invention is to provide a manifold gasket as stated above, wherein the manifold gasket can properly absorb change of sealing pressure applied thereto, which is caused by deformation of the gasket attaching portion due to heat as well as a poor rigidity of the gasket attaching portion.
A still further object of the present invention is to provide a manifold gasket as stated above, wherein the manifold gasket can properly respond and operates to high and low temperature due to operation and non-operation of an engine.
A still further object of the present invention is to provide a manifold gasket as stated above, wherein the structure is simple and the gasket can be economically manufactured.
Further objects and advantages of the present invention will be apparent from the following description of the invention.